Directly heated cathode structure



Sept. 22, 1953 B. D. KUMPFER DIRECTLY HEATED CATHODE STRUCTURE Filed May 1, 1950 FIG.2

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Patented Sept. 22, 1953 pnrsc'rpr HEATED CATHODE, STRUCTURE Beverb D. Kumpfer, Spring Lake Heights, N. J., assignor to. the United States of America as repre ented by th cretary of the Army Application May 1, 1950, Serial No. 159,351

4 Claims. (Cl. 313-346) (Granted under Tit 5, U. S. (lode (1952),

sec. 266) i The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment to me of any royalty thereon.

This invention relates to improvements in cath-. ode structures, and more particularly to directlyheated cathodes for embodiment in subminiature magnetrons.

In the conventional cathode structure, heat from a filament is transferred or conducted to av thermionically-active surface through an inter posed layer of insulating material or through the wall of a metal cylinder on the outside surface of which thermionically-active material is deposited. These are known as indirectly-heated cathodes, examples of which are disclosed in Patent No. 2,014,787, issued September 17, 1935, to Smithells et a1, and in Patent No. 2,194,678, issued March 2.5, 19.40, to Sommers. Due to the fact that heat is imparted to the thermionically-active material indirectly, the thermal efiiciency of the conventional, indirectly-heated cathodes is relatively low. The construction or fabrication of the indirectly-heated cathodes, furthermore, i such that it would be practically impossible to make them in very small sizes for embodiment in sub miniature magnetrons, for example. Also, the cathode structures of the prior art have a. relatively short life under severe operating conditions suchas exist in subminiature magnetrons where high ruggedness and large emissive surface, in proportion to overall size, are required.

With the foregoin in mind, it is one of the objects of my invention to provide an improved cathode structure adapted particularly for use in subminiature magnetrons, and which in any case, has; a longer effective life than the variou cathode constructions of the prior art, under the same operating conditions.

Another object of my invention resides in the provision of an improved cathode structure which has advantages over those proposed heretofore in the way of higher thermal efficiency and greater ruggedness of construction.

Another object of my invention is the provision of an, improved cathode structure for magnetrons which not only can stand. up under the severe operating requirements of high ruggedness. and high emissive rate in proportion to size, but, which lends itself also to fabrication or manufacture in very small sizes such as are required for embodiment in subminiature magnetrons.

-Other objects and advantages will hereinafter appear.

For the purpose of illustrating my invention,

2. emb dim nt thereof is shown in the drawin where n Figu e l is an enlarged, longitudinal sectional View of a cathode constructed and operating in accordance with my invention, the section being take the ine i| in Fi ure 3;

Figure 2 is a front, elevational view oi Figure 1;

Figure 3 is a plan view of Figure 2; and

Fi ure 4. is a View similar to Fi ure 1, but on a reduced scale and showing a, practical application of my invention.

For the purpos of simplification in di clos ng my invention, the step-by-stel) oper tionsinmaking or fabricating a cathode structure embodying the same, Will first be, explained with reference, particularly, to Figure. 1;. Alumina is, first applied by sprayin or dippin to a sup ort. m m er in the form of a. rod it, after which th rod so coated is, baked in an atmosphere of hydrogen to convert or change the alumina. to. a hard ceramic subst n e he member or. su port red It is hus charaoterized by the fact that the outside surface thereof is of insulating material. In one application of my invention such as is shown in Figure 4 and which has given satisfactory results in subminiature magnetrons, the rod Ill was of tungsten with an outside diameter of .007 inch, and, its length appr ximately .35- in h. s in this particular application the thickness or depthv of the insulating layer or coating ll was .003 inch, and it extended over substantially the entire length of, rod [0, as shown in Figure 4.

The heater for my improved cathode i in the form of awire wound about rod in to provide a filament 12. In the particular application of my invention referred to above, nickel wire having a diameter of two thousandths of an inch was used for the filament ii. In applyin this Wire to red it) to form the heater or filament i2, one end is first spot-welded to a protective nickel cap l4 fitted over the upper end of the. rod and in electrical contact with the latter, as shown. This end of, wire, it may, however, be spot-welded directlyto the upper end of rod I 6, as represented at 15 in Figures 2 and 3. The filament Wire l2 t e about rod wto make ppro mately two hun red fifty turns per linearinch. The resp ive adj cent; ns of he. h l u formed are her fore s a ed, for e specified gauge of Wire used, approximately .002 inch. The other end of the Wire is then spot-Welded, as represented at It, to a nickel sleeve I1 fitted onto the lower end of rod I 0 and electrically-insulated from the latter by the ceramic coating II.

To complete the assembly or fabrication, thermionically-active material I8 is applied by spraying or dipping, and as more clearly illustrated in Figure 1, serves the additional function of bonding the turns of wire 52 to the insulating ceramic coating 1% on the central, support rod iii. In Figures 1, 2 and 3 the thickness or depth of the emission coating 48 is shown as not quite covering completely the wire helix. In Fig. 4, the thick uses or depth of the coating it, which was composed of triple carbonates, was approximately .002 inch. V

In the construction shown in Figure 4, a nickel sleeve 13 fitted over the assembly, imparts additional rigidity and strength at the junction of filament it with sleeve ii, and also protects the spot-weld connection between the latter two parts.

The sleeve i! and the lower end of rod l0, both of which are disposed at one and the same end of my improved. cathode structure, provide, respectively, terminal connections for currentsupply to filament l2 from any suitable source such as a battery represented at 20. In the construction shown in Figure 4, parts 2i and 22 are spot-welded, respectively, to sleeve ll and rod l0, and serve as terminals for more conveniently making connection to the battery 20 or other power-supply.

While my improved cathode structure has been described as being especially adapted for use in magnetrons, it may be used to equal advantage in any of the many difierent, present-day types of thermionic tubes. An important aspect of my invention resides in the novel construction,

arrangement and dimensional relations of the respective parts to each other, all of which makes practical an otherwise extremely difiicult cathode construction, results in a unit lending itself to reasonably easy manufacture in the very small sizes required for use in subminiature magnetrons, and has at the same time the essential operating characteristics and capabilities for prolonged use under the severe operating conditions imposed in magnetrons.

In some forms of cathode constructions embodying my invention, it may be more expedient to use for the filament l2 a metal in strip form, instead of the more conventional wire or circular form shown. There may be other alternatives such as using molybdenum instead of tungsten for the rod It, and any other suitable materials in substitution for those specified for the respective parts.

While but one embodiment of my invention has been shown and described, it will be understood Y that various modifications such as in the size, shape and arrangement of the parts, may be made Within the conception of those skilled in the art without departing from the spirit of my invention or the scope of the claims.

What is claimed is:

1. A directly heated cathode comprising an electrically conductive rod, insulating means disposed on the outside surface of said rod, a wire wound about the insulated rod so as to provide a filament, a cap disposed about one end of said rod and electrically connecting it to said filament wire, thermionically-active material intimately associated with and disposed between adjacent turns of said wire along a given length of said insulated rod and bonding said filament wire thereto, first sleeve means disposed about the other end of said insulated rod and electrically connected to said filament wire, second sleeve means disposed about said first sleeve means as well as a portion of said filament, for providing protection for the junction of said filament and said first sleeve, and means disposed at said other end of said rod and electrically connected thereto and to said first sleeve, for supplying current to said filament.

2. A directly heated cathode assembly comprising a rigid inner conductor, a layer of insulating material bonded to the outer surface of said conductor, a Wire wound about the insulated conductor so as to provide a filament, thermionically-active material disposed between adjacent turns of said filament bonding said filament to said insulated conductor, and a pair of current- :supply terminals at one end of said assembly, one terminal being electrically connected to one end of said conductor and the other terminal being electrically connected to a like end of said wire, the other end of said wire being electrically connected to the other end of said conductor.

3. A directly heated cathode structure comprising a conductive member at least the outside surface of which is of insulating material, a heater in the form of a filament wound about said member, thermionically-active material disposed between adjacent turns of said filament along a given length of said member and bonding said filament thereto, a pair of terminals disposed at one and the same end of said structure and respectively in contact with said member and said heater for providing terminal connections for current-supply of said filament, and means electrically connecting said filament to said member at the ends thereof remote from the terminal connection end of said structure.

4. A directly heated cathode structure comprising a conductive rod, a layer of insulating material bonded to the outer surface 01 said rod, a wire wound about the insulated rod and in contact with said insulating material to provide a filament, thermionically-active material disposed between adjacent turns of said wire and extending radially outwardly beyond said wire along a given length of said rod bonding said filament to said insulating material, and a pair of terminal means disposed at a given end of said structure, said terminal means being respectively in electrical contact with said rod and said wire, and providing terminal connections for current-supply to said filament, said filament being electrically connected to said rod at the end of said cathode structure remote from the terminal connection end of said structure.

BEVERLY D. KUMPFER.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,813,704 Lederer July 7, 1931 1,942,080 Young Jan. 2, 1934 2,014,787 Smithells et al Sept. 17,1935 2,501,089 Pomerantz Mar. 31, 1950 

